1. Field of the Invention
The present invention relates to an optical network analyzer for measuring the amplitude characteristics and group delay time dispersion characteristics of an optical circuit device.
2. Description of the Related Art
As is well known, the optical fibers utilized in an optical communication line have come to play a more and more important role in the communication infrastructure of an intellectual information-oriented society, and have therefore required further improvement. In particular, optical fibers enabling both a high data transmission speed and a long repeater-to-repeater distance have come to be required, so as to meet the demand for an economic optical communication line.
In recent years, progress has been made in the technology for developing a light amplifier that employs optical fibers doped with Er (erbium). This type of light amplifier can compensate for the loss of an optical transmission line, and is therefore expected to considerably lengthen the repeater-to-repeater distance. Progress has also been made in the technology for developing large-capacity optical communication lines wherein a number of optical frequencies are multiplexed as carriers, as in a coherent communication system.
In these next-generation optical communication systems, it is necessary to employ optical circuit devices wherein the transmission characteristics are defined at high level. For example, an optical circuit device for compensating for group delay dispersions and an optical multiplex division circuit are required. It is also necessary to accurately measure or evaluate the group delay time dispersion characteristics and amplitude characteristics of the entire optical transmission system (including an optical fiber transmission line and optical circuit devices).
With the present technology, however, it is very difficult to measure the group delay time dispersion characteristics of an optical circuit device with high optical frequency resolution and in an optical frequency band in the range of several hundred gigahertz (GHz), and there is not means available for accurately measuring an important optical frequency characteristic, such as a central optical frequency of the optical circuit device.